Test MethodDetermination of the glass transition temperature in thin polymeric films used for microelectronic packaging by temperature-dependent spectroscopic ellipsometry

We characterized the glass transition temperature Tg of thin polyimide films by temperature-dependent spectroscopic ellipsometry and compared the results to DSC measurements of the bulk polymer. The effect of the curing temperature on Tg and the thermal expansion α(T) was analyzed. An improved ellipsometric data evaluation was used to get most precise and reliable Tg data. Tg increased with increasing curing temperature, while the bulk Tg was considerably lower than the thin film Tg. Both observations are attributed to the temperature sensitive release of the imidization by-product 2-hydroxyethyl methacrylate (HEMA) and crosslinker components as well as decomposition products from the material. Variation in the curing temperatures of 230-380 °C led to an increase in the Tg of 34 °C.